This invention relates generally to the ramping or upgrading in performance of an operating superconducting magnet, and more particularly relates to a method and apparatus providing improved high current connections to a superconducting magnet. As is known in the art, a superconducting magnet surrounded with liquid helium in an evacuated jacket, can operate with little maintenance over extended time periods when the apparatus has been constructed with high integrity to minimize heat gain and thereby to reduce consumption of helium.
Nevertheless, from time to time it becomes necessary to increase or decrease the superconductive current, that is, to charge or ramp, the superconducting magnet to restore a level of electrical performance that has slowly deteriorated, or to decrease the current to zero for service of other components. The interval between rampings in a well designed system may be a year or more. However, a need for ramping does inevitably arise.
The cryostat system including the magnet is designed with recognition that during the ramping procedure a charge of high current will be input to the magnet through connection terminals that are provided within the cryostat and are accessed, generally, through the top of the cryostat chamber. Access to the current terminals from the sides of the magnet or from below could also be provided. A fill port for helium is also generally provided at the top of the cryostat.
Desirably, permanent leads would be provided on the magnet, connected fixedly to terminals readily accessible from the outside of the cryostat for ramping purposes. However, this is an impractical concept. Such leads permanently extending from the cryogenically cold magnet towards the outer surfaces of the cryostat at room temperature would be a conduit for in-leakage of thermal energy that would result in substantially increased consumption of helium. Especially considering that ramping is a procedure that may not occur but once every year or two, it is desirable that minimization of heat in-leakage be achieved with priority over convenience in making electrical lead connections when ramping the superconducting magnet. Thus, it has become an accepted practice to use ramping leads that are connected only for actual ramping procedures, and then are removed.
A problem arises in many installations of superconducting magnets as a result of this necessity to occasionally adjust the magnet current. Namely, the requirement for access to the interior of the cryostat may affect ceiling space requirements at the installation. Clearance at the top of the cryostat/magnet assembly to permit the occasional access of ramping leads to the magnet in many installations will take away space that otherwise could be used for containing a larger cryostat/magnet assembly or a lower ceiling. In fact ceiling restrictions are an important limitation when installing magnets in a pre-existing facility. Thus the need for convenient ramping using high current carrying leads and the desire to optimize the magnet installation size are in contradiction.
What is needed is a method and apparatus for use in ramping a superconducting magnet whereby high current leads may be connected and disconnected to and from the magnet with reduced adverse effect on ceiling space requirements for the installation.